A hybrid vehicle comprises an internal combustion thermal engine, which transmits torque to the driving wheels by means of a transmission provided with a gearbox coupled to a clutch, and at least one electric machine, which is electrically connected to an electric storage system and mechanically connected to the driving wheels.
The following is possible while traveling: either a thermal operating mode, in which the torque is generated only by the thermal engine and the electric machine may possibly work as a generator for recharging the storage system; or an electric operating mode, in which the thermal engine is off and the torque is generated only by the electric machine working as a motor; or a combined operating mode, in which the torque is generated both by the thermal engine and by the electric machine working as a motor. Furthermore, in order to increase the overall energy efficiency during all steps of decelerating, the electric machine may be used as a generator for a regenerative deceleration in which the kinetic energy possessed by the vehicle is partially converted into electricity, which is stored in the electric storage system, instead of being completely dissipated in friction.
On some hybrid vehicles, the gearbox comprises a circulation pump for circulating lubricating oil through the gears of the gearbox so as to ensure adequate lubrication of the gears. Furthermore, in the case of a hydraulically actuated, automatic manual transmission (commonly named “AMT”), the gearbox also comprises an actuation pump, which supplies the hydraulic pressure needed for operating the hydraulic actuators engaging and selecting the gears and controlling the clutch.
In the currently manufactured gearboxes, the gearbox pumps are actuated by an auxiliary activating shaft, which takes motion from the drive shaft (possibly with the interposition of a transmission shaft), i.e. upstream of the clutch, so that it is always actuated when the clutch is open. This condition makes the mechanical connection of an electric machine to a shaft of the gearbox less convenient, because in case of electric traction (i.e. when the thermal engine is off), the clutch must remain closed to actuate the pumps, and therefore the thermal engine is also rotatably fed (with considerable frictions and inertia). Furthermore, because the electric machine cannot be rotated when disconnected from the thermal engine (under these conditions, there would be no lubrication of the gearbox and especially no hydraulic pressure required to actuate the clutch), the electric machine may not be used as a starter motor of the thermal engine, because in order to use the electric machine as a starter motor of the thermal engine, the electric machine should be rotated at high speed before connecting the electric machine to the thermal engine for the electric machine to store a high amount of kinetic energy.
In order to solve the above-described problem, it has been suggested to make the activating shaft of the gearbox pumps mechanically independent from the drive shaft, and to actuate the gearbox pump activating shaft by means of a dedicated electric motor; however, this solution normally requires re-designing the gearbox, with high development costs, and is not very efficient from the energy point of view, because when the thermal engine is running (i.e. for most time of use of the vehicle), using part of the torque generated by the thermal engine is more efficient for directly actuating the auxiliaries rather than converting part of the torque generated by the thermal engine into electricity, which is transformed back into mechanical torque by an electric motor. Furthermore, arranging an electric motor mechanically coupled to the activating shaft of the gearbox pumps is not easy, because the gearbox zone has small free spaces, it is quite hot due to the heat generated by friction inside the clutch and the gearbox, and it is not very ventilated as it is normally located in the middle of the vehicle.
Patent application EP1216871A2 and patent application US2008087487A1 describe a transmission for a road vehicle with hybrid propulsion comprising: a twin-clutch gearbox provided with two primary shafts, a secondary shaft, and a lubrication pump; two clutches connected to the primary shafts and having a normally conductive part, which may be connected to a drive shaft of a thermal engine; a reversible electric machine having a shaft mechanically connected to one of the two primary shafts; a first mechanical transmission, which transmits the motion from the normally conductive part of the clutch to the lubrication pump and comprises a first freewheel; and a second mechanical transmission, which transmits the motion from the shaft of the electric machine to the lubrication pump and comprises a second freewheel.